Energy absorber

ABSTRACT

An energy absorber comprises housing means ( 1 ), a store ( 15 ) of plastically deformable material ( 8 ) mounted in the housing means and having an endstop ( 27 ), means ( 3 ) for attaching the energy absorber to a structure, means ( 10 ) for attaching the plastically deformable material ( 8 ) to a structure, and means ( 7, 5, 6 ) responsive to a predetermined tensile load effective to deploy said plastically deformable material ( 8 ) in a controlled manner from its store whereby said material ( 8 ) is permanently plastically deformed during said deployment, thereby absorbing energy. The energy absorber is able to support a load at least twice the predetermined tensile load when further deployment of the material ( 8 ) is prevented by the endstop ( 27 ).

[0001] The present invention relates to an energy absorber and, inparticular, to an energy absorber that absorbs tensile energy anddeploys irreversibly at or close to a constant force.

[0002] Tension energy shock absorbers are often used to assist theabsorption of energy in constrained or partially constrained lines. Forexample, fall arrest applications require energy from a falling body tobe absorbed by a line such as a rope or wire which is usually attachedto a strong structure at one end or both ends. In such situations, it isdesirable to achieve a low combination of stretch in the line and linetension. Lowering line stretch reduces the distance the body fallsbefore arrest, and also reduces the fall energy. Lowering line tensionreduces the loading on the line and also on the anchor or anchorsconstraining the line. Another example of energy absorption inconstrained lines is vehicle crash barriers that absorb vehicle kineticenergy. Lower line stretch reduces the degree to which a vehicle canmove across a crash barrier. Lower line loads reduce the likelihood ofline and/or anchorage failure in the event of a crash.

[0003] The amount of energy absorption in constrained or partiallyconstrained lines is determined by the product of stretch in the lineand the line tension. Typically, line stretch is elastic such that theamount of stretch increases in proportion to the tension in the line.The energy absorbed is therefore the average line tension or half themaximum line tension multiplied by the stretch. However, in order tominimise the combination of line stretch and line tension, the idealline system would absorb energy by stretching at a predetermined linetension where the energy absorbed is the predetermined line tensionmultiplied by the line stretch. This would absorb the same energy as theelastic line system for a given maximum line tension but require onlyhalf the line stretch. Also, such a system would be able to limitmaximum line tension to the predetermined force at which stretch occurs.

[0004] In practice, it is difficult to achieve this ideal, butsignificant improvement can be made in energy absorption efficiency withrespect to the combination of line stretch and line tension by combininglow stretch line with an energy absorber that deploys by stretching at apredetermined force. If the extent of deployment stretch in such anabsorber is sufficiently large, it could also effectively limit linetension to the predetermined deployment force for all foreseeable energyabsorption situations. This is important for establishing with a highdegree of certainty safe design criteria for line systems and anchors.

[0005] In energy absorbers for use in fall arrest systems it is a normalrequirement that the energy absorber be able to support double the peakdeployment force after full deployment.

[0006] In conventional energy absorbers that deploy at a constant force,the component which is deployed is typically straight, being housedwithin a further straight component prior to deployment. The overalllength of such an absorber prior to deployment is therefore greater thanthe extent of deployment. Such energy absorbers typically consist of acomponent, preferably having a spherical or part-spherical leadingportion, which is pulled through a length of tube having a bore smallerin diameter than the outer dimension of the leading portion of saidcomponent, such that a force is required effectively to extrude the boreof the tube. One such energy absorber is described in the presentApplicants granted European Patent No. EP 0 605 538.

[0007] In view of the foregoing analysis, it will be clear to personsskilled in the art that, in applications in which large deploymentextents are required, the overall length of the energy absorber alsoneeds to be large.

[0008] This is undesirable, not only from the point of view of cost, butalso because in many applications such as fall arrest it is important togain access to a constrained or partially constrained line close to theconstraining anchors. Typically, large deployment extents are useful forcontaining line loads and also ensuring that line loads never exceed thepredetermined deployment force of the energy absorber for allforeseeable situations, and provide a useful energy absorption surplusas a contingency against unforeseeable circumstances.

[0009] It is therefore an object of the present invention to provide anenergy absorber which gives a long deployment stroke without occupyingan inordinate linear extent.

[0010] According to the present invention, there is provided an energyabsorber comprising housing means, a store of plastically deformablematerial wound in a coil and having an endstop at one end and mounted insaid housing means, means for attaching the energy absorber to a firststructure, means for attaching the plastically deformable material to asecond structure, and means responsive to a predetermined tensile loadbetween the first and second structures effective to deploy saidplastically deformable material in a controlled manner from its storewhereby said material is permanently plastically deformed during saiddeployment, thereby absorbing energy, the energy absorber being able tosupport a load at least twice the predetermined tensile load whenfurther deployment of said material is prevented by the endstop.

[0011] Preferably, the plastically deformable material is a length ofyielding material such as metal, the length being relative to themaximum extension required for absorbing energy. One end of the lengthof material preferably has provision for attaching the material to aline or rail anchorage and, close to such attachment provision, thematerial is preferably constrained in a non-linear path by a structurethat also has provision for attachment to a line or anchorage. In suchan arrangement, when the material is pulled relative to the structure,the material is forced by the structure to move in a non-linear path andits movement is therefore resisted primarily by the reluctance of thematerial to yield. Movement of the material is enabled when the pullingforce is sufficiently great to overcome the yielding resistance, thushaving the effect of absorbing energy as a result of the product of thetensile force needed to overcome the resistance to movement of thematerial and the extent of movement of the material relative to thestructure. The tensile forces required to effect deployment aresubstantially determined by the yielding and therefore plasticdeformation properties of the material, its section shape and the degreeof non-linearity of its path as constrained by the housing means.

[0012] The length of material can have any cross-section such asrectilinear, round, tubular or any other shape. In some embodiments, thesection shape can vary along the length of the material, for example, inapplications in which it is desirable to vary the resistant forcebetween the housing means and the material. The non-linear path of thematerial when pulled and as constrained by the housing means is definedby two dimensional inclinations.

[0013] Preferably, the elements of the housing means constraining thepath of movement of the material when pulled relative to the housingmeans can be circular shafts or rollers, each roller rotating about itsown axis, or any other shape constraining the path of the material.

[0014] The invention will now be described by way of example only withreference to the drawings, in which:

[0015]FIG. 1 is a perspective view of a first embodiment of theinvention with the length of material spirally wound;

[0016]FIG. 2 shows a side elevation of the embodiment depicted in FIG.1;

[0017]FIG. 3 shows a first perspective view of a second embodiment ofthe invention;

[0018]FIG. 4 shows a second perspective view of the embodiment of FIG.3;

[0019]FIG. 5 shows a side elevation of the third embodiment of theinvention ready for deployment;

[0020]FIG. 6 shows a side view of the embodiment of FIG. 5 afterdeployment;

[0021]FIG. 7 shows a side view of a fourth embodiment of the inventionready for deployment;

[0022]FIG. 8 shows a side view of the embodiment of FIG. 7 afterdeployment;

[0023]FIG. 9 shows an endstop structure suitable for use in theembodiment of FIG. 7;

[0024]FIG. 10 shows a side view of a fifth embodiment of the inventionready for deployment;

[0025]FIG. 11 shows a side view of the embodiment of FIG. 10 afterdeployment;

[0026]FIG. 12 shows a perspective view of a first endstop structuresuitable for use in the embodiment of FIG. 1;

[0027]FIG. 13 shows a perspective view of a second endstop structuresuitable for use in the embodiment of FIG. 1;

[0028]FIG. 14 shows a side view of a sixth embodiment of the inventionready for deployment;

[0029]FIG. 15 shows a side view of the embodiment of FIG. 12 afterdeployment;

[0030]FIG. 16 shows a side view of a seventh embodiment of the inventionready for deployment;

[0031]FIG. 17 shows a side view of the embodiment of FIG. 14 afterdeployment;

[0032]FIG. 18 shows a side view of an eighth embodiment of the inventionready for deployment;

[0033]FIG. 19 shows a side view of a ninth embodiment of the inventionready for deployment;

[0034]FIG. 20 shows a side view of the tenth embodiment of the inventionready for deployment;

[0035]FIG. 21 shows a side view of an eleventh embodiment of theinvention ready for deployment;

[0036]FIG. 22 shows a first side view of a twelfth embodiment of theinvention employing a helical coil ready for deployment;

[0037]FIG. 23 shows a second side view of the embodiment of FIG. 22;

[0038]FIG. 24 shows a detail view of the endstop of FIG. 22 afterdeployment;

[0039]FIG. 25 shows a side view of a thirteenth embodiment of theinvention employing a helical coil ready for deployment;

[0040]FIG. 26 shows an end view of the embodiment of FIG. 25;

[0041]FIG. 27 shows a side view of a fourteenth embodiment of theinvention employing a helical coil;

[0042]FIG. 28 shows a second side view of the embodiment of FIG. 27;

[0043]FIG. 29 shows a perspective view of an fifteenth embodiment of theinvention ready for deployment; and

[0044]FIG. 30 shows the embodiment of FIG. 29 after deployment.

[0045] As shown in FIGS. 1 and 2, an energy absorber has a structurecomprising a housing means formed of plates 1 and 2 that are spacedapart and fixed to pins 5, 6 and 7 such that plates 1 and 2 are rigidlylinked. Fixing means 3 and 4 are provided at one end of the plates forattaching them to a rigid anchor or wire or rope termination. Length ofmaterial 8 is a strip material that is wound into a spiral 15 and bentat 16 and 17 to fit beneath pin 5 and above pin 6, respectively. Thelength of material 8 is provided with attachment means 9 at one end forattaching to a rigid anchor or wire or rope termination and with anendstop 27 at the other end to prevent the material 8 being separatedfrom the housing. The spiral winding enables a long length of materialto be stored within a relatively short linear space. Plate 10 is held tothe end of length of material 8 by means of rivets 11 and 12 in order tostrengthen attachment means 9. In some embodiments not illustrated here,it may not be necessary to include plate 10. Alternatively, plate 10could be fixed to the end of length of material 8 by some other means,such as by welding.

[0046] When the energy absorber is required to absorb energy, anincreasing tension force is applied to attachment means 3 and 4, and 9in the direction of arrows 13 and 14 until the applied force becomessufficiently high to pull material 8 around pins 5 and 6 such that theabsorber extends to absorb energy. Pin 7 assists in unwinding spiral 15.

[0047] In order to allow the tension force required to deploy thematerial 8 and so extend the absorber to be kept constant the degree ofbending of the material 8 at bends 16 and 17 around pins 5 and 6 must bekept constant. The location of the pin 7 controls the angle at which thematerial 8 is supplied to the pin 5 to be fixed as the material 8deploys from the spiral 15 and so keeps the tension force constant.

[0048] The endstop 27 is formed by additional plates 28 of materialrivetted to the faces of the material 8 close to the end of material 8to provide a thickened section which becomes trapped between pins 5 and6 to provide a limit to the deployment of material 8. The endstop 27 isrelatively substantial in order to allow the endstop 27 to retain thematerial 8 attached to the housing, and thus to the support structurethrough fixing means 3 and 4, under a load of at least double thedeployment tension force after full deployment of the material 8.

[0049] If material 8 is consistent in nature and cross-section, thetension force required to move the material in the direction of arrow 14should be approximately constant in relation to the degree of movementof material 8.

[0050] The energy absorption as the absorber extends is produced by theunwinding of the material from the spiral and by the bending andsubsequent straightening of the length of material 8 around the pins 5and 6.

[0051] It might be expected that the tension force would increase as thematerial 8 unwinds from the spiral 15 because the curl diameter of thespiral decreases as the material 8 is deployed resulting in a greaterdegree of bending of the material 8 being required. However, in practiceno such increase in the tension force has been observed. It is believedthat this is because the degree of bending required to straightenmaterial from the spiral is very much smaller than the degree of bendingand re-bending taking place around the pins 5 and 6 at the bends 16 and17 so that any increase in the tension force is marginal. Nevertheless,it is still expected that such an increase in tension force as thematerial 8 is deployed will occur, particularly where the degree ofbending at the bends 16 and 17 is relatively small and the coil 15 has arelatively small radius.

[0052] When the energy absorber is intended for use in a fall arrestsystem the energy absorber will normally be dimensioned so that theenergy absorbed by deploying the material 8 fully until the endstop 27becomes trapped between the pins 5 and 6 is significantly greater thanthe maximum amount of energy which is expected to require absorption ina fall arrest event. Thus, in order to avoid excessive line tension andphysical shock to users, where the energy absorber is to be used in afall arrest system it would normally be expected that the fall would bearrested and deployment of the material 8 stopped before the endstop 27was reached. However, the endstop 27 is a safety feature preventingrelease of the material 8 from the housing even if the energy absorptionrequirements in the fall arrest situation prove to be greater thanexpected. Further, the endstop 27 provides a positive limit on extensionof the material 8 from the housing so that the requirement that afterfull deployment the energy absorber still be able to support twice thepeak tension force encountered during deployment can be met.

[0053] It should be noted that the provision of such endstops is notnormal in energy absorbers.

[0054] One potential source of undesirable variation in the tensionforce as the material 8 deployed from the energy absorber shown in FIGS.1 and 2 is that the tension in the material 8 as it deploys will tend topull the coil 15 towards the pin 7, resulting in a varying frictionalload, and possibly resulting in the coil 15 riding over the pin 7. Suchoverriding of the pin 7 by the coil 15 would significantly change thegeometry of the system and could result in significant changes in theload.

[0055] A second alternative embodiment of the invention is shown inperspective in FIGS. 3 and 4.

[0056] The second embodiment shown in FIGS. 3 and 4 is similar to thefirst embodiment shown in FIGS. 1 and 2 except that an aperture 20 isformed in the side plate 2. A matching aperture 20 is also formed in theside plate 1, but this is not visible in the figures.

[0057] The endstop 27 of the material 8 is formed into a T-shape so thata lateral extension 21 of the material 8 extends into the aperture 20. Acorresponding lateral extension 21 in the opposite direction extendsinto the aperture 20 formed in the opposite side plate 1, but again thisis not visible in the figures.

[0058] The apertures 20 are sized so that the projections 21 fit looselywithin the apertures 20 allowing the spiral 15 of material 8 to rotatefreely as the material 8 is deployed from the housing. The loose fit ofthe projections 21 within the apertures 20 constrains the movement ofthe spiral 15 sufficiently to prevent the spiral 15 overriding the pin 7but allows the position of the spiral 15 to float to compensate forchanges in the radius of the coil 15 as the material 8 deploys.

[0059] This floating movement of the coil 15 allows the point at whichthe outermost layer of the material 8 is detached from the bulk of thecoil 15 to remain approximately fixed relative to the position of thepin 7 throughout the deployment of the material 8. The helps to keep thedegree of bending experienced by the material 8 close to constantthroughout the deployment so that the tension force remains as close aspossible to a constant value.

[0060] The projections 21 at the end of the material 8 passing into theapertures 20 also provides an endstop for the material 8. When thematerial 8 is fully deployed further movement of the material 8 out ofthe housing 1 is stopped by engagement of the projections 21 in theapertures 20. However, in this arrangement it will normally be preferredfor safety reasons to also provide a back-up endstop 27 similar to thatshown in the first embodiment of FIGS. 1 and 2.

[0061] Although the second embodiment shown in FIGS. 3 and 4 isgenerally effective, there are disadvantages to the use of projectionsat the end of the material 8 passing into apertures in the housing sideplates.

[0062] The first disadvantage of the use of projections at the end ofthe material 8 passing into apertures is that contact between theprojections and the sides of the apertures as the material 8 deploys andthe spiral coil rotates can generate significant amounts of friction. Aswill be explained in more detail below frictional forces acting on thematerial 8 are generally undesirable. Friction generated by contactbetween the projections and the sides of the apertures is particularlyundesirable because due to the rotation of the spiral coil the contactand resulting amount of frictional force is intermittent andunpredictable and will inevitably produce variations in the deploymentforce of the material 8.

[0063] A further disadvantage of the use of projections passing intoapertures in the side plates is cost. Such an arrangement is relativelycostly to manufacture compared to the other embodiments describedherein.

[0064] However, despite these disadvantages the second embodiment canusefully be employed.

[0065] In the second embodiment the housing structure is different fromthe first embodiment. In the second embodiment the housing is formed byside plates 1 and 2 which are formed by bending a single plate into aU-shape such that the side plates 1 and 2 and one end of the housing arean integral unit. In addition to the pins 5, 6 and 7 which interact withthe material 8, additional structural pins 24 and 25 are provided toensure that the side plates 1 and 2 are rigidly linked and the housingprovides a rigid structure but these pins 24 and 25 do not cooperatewith the deployed material 8.

[0066] The pins 24 and 25 project beyond the side plates 1 and 2 tosecure an exterior casing (not shown in FIG. 4) to the housing.

[0067] Further, instead of fixing means 3 and 4 in the first embodimentthe housing of the second embodiment is fixed to a rigid anchor or wirerope termination by the anchor or a rope being passed through anaperture in the end of the U-shape forming the housing structure.

[0068] Further, in the second embodiment an alternative terminationmeans 26 for the end of the material 8 for attaching to a rigid anchoror wire rope termination is shown. A pair of plates 32 are held to theend of a length of material 8 by means of rivets and the attachmentmeans 26 are provided as holes through the opposed plates 32.

[0069] A third embodiment of the invention is shown in FIGS. 5 and 6which both show side views of a third embodiment of the energy absorber.In FIG. 5 the energy absorber is shown before operation, that is, in anun-deployed condition while in FIG. 6 the energy absorber is shown afterfull deployment with the material 8 fully extended from the housing.

[0070] The energy absorber according to the third embodiment is similarto the absorber of the first embodiment having side plates 1 and 2without the aperture 20 provided in the absorber of the secondembodiment.

[0071] A U-shaped plate 22 is located between the side plates 1 and 2adjacent the rest position of the coil 15.

[0072] When the material 8 is deployed from the absorber the tension inthe material 8 will tend to pull the coil 15 towards and over the pin 7.Such a movement of the coil 15 will be prevented by the side plate 22.As the material 8 deploys from the coil 15 the body of the coil 15 willbe urged into contact with the pin 7 and the side plate 22 to preventthe coil 15 overriding the pin 7.

[0073] It is preferred for the endstop 27 to be able to pass between thepin 7, pin 5 and side plate 22 and to be held between the pins 5 and 6to provide its endstop action.

[0074] A fourth embodiment of the invention is shown in FIGS. 7 and 8which again show side elevation views of the absorber with FIG. 7showing the absorber when the material 8 is un-deployed and FIG. 8showing the absorber when the material 8 is fully deployed.

[0075] The endstop arrangement of the fourth embodiment is shown indetail in FIG. 9.

[0076] In the fourth embodiment the housing includes a substantiallyU-shaped side plate 22 similar to that shown in the third embodiment andhaving the same function of preventing the spiral 15 overriding the pin7 and cooperating with the pin 7 to control the position of the spiral15 as the material 8 is deployed.

[0077] In the fourth embodiment there are apertures 23 in the sideplates 1 and 2 (only the aperture 23 and side plate 1 is shown in thefigures, the aperture in the side plate 2 will be a mirror image).

[0078] The endstop 29 of the material 8 in the fourth embodiment has twoplates of material 30 rivetted to the two faces of the material 8 toprovide an endstop section close the end of the material 8. The plates30 extend beyond the material 8 in a lateral direction so that each ofthe plates 30 provides a projection 31 which extends into one of theapertures 23.

[0079] Unlike the arrangement of the second embodiment, the projections31 into the apertures 23 are intended only to provide an endstop and notto provide any guiding or localising function to control the position ofthe spiral 15, in this embodiment the location of the spiral 15 iscontrolled by the side plate 22. Accordingly, the apertures 23 are sizedand shaped so that they do not constrain movement of the coil 15 as thematerial 8 is deployed from the housing.

[0080] When the material 8 has fully deployed from the housing theendstop 29 will move until the projections 31 contact the edges of theapertures 23 and the endstop 29 will then stop further deployment of thematerial 8 from the housing 1. The use of rivetted plates 30 to providethe endstop 29 means that the endstop 29 is significantly thicker thanthe bulk of the material 8 and this arrangement is preferred because itallows a back-up backstop arrangement to be provided for safety by theendstop 29 being trapped between the pins 5 and 6 similarly to thearrangement of the first embodiment.

[0081] In the fourth embodiment an additional pin 46 is providedadjacent to the pin 6. The pin 46 connects the side plates 1 and 2adjacent to the pins 5 and 6 and helps to reinforce and stabilise thehousing structure in this region to ensure that the loads on the pins 5and 6 can be transferred into the side plates 1 and 2. Further, the pin46 is arranged so that the material 8 passes between the pins 6 and 46.Thus, the additional pin 46 can assist in stabilising and controllingthe degree of bending of the material 8 so that the extension force canbe held constant. Further, trapping of the thickened endstop 29 betweenthe pins 6 and 46 provides a further back-up endstop arrangement foradditional safety. Note that the provision of the pin 46 is notessential for the arrangement of the fourth embodiment. A pin similar tothe pin 46 could be provided in any of the other embodiments if desired.

[0082] A fifth embodiment of the invention is shown in FIGS. 10 and 11in side elevation with the material 8 ready to be deployed in FIG. 10and the material 8 fully deployed from the housing in FIG. 11.

[0083] The fifth embodiment is similar to the third embodiment with theaddition of an extra pin 33 opposed to the pin 7.

[0084] When the material 8 is fully deployed the pins 7 and 33 willprevent further movement of the material 8 by trapping the thickenedendstop 27 between them. In this case the pins 5 and 6 will act as aback-up endstop arrangement for safety, trapping the thickened endstop27 between them if the pins 7 or 33 should fail.

[0085] In addition to trapping the endstop 27 the pin 33 cooperates withthe pin 7 to control the movement of the material 8 as it moves towardsthe pins 5 and 6, further ensuring a constant tension force duringdeployment of the material 8. This prevents excessive movement of thematerial 8 which could cause the deployment tension on the material 8 tochange. Such prevention of excessive movement of the material 8 isparticularly important when the material 8 is undergoing heavyacceleration, for example during a fall arrest event.

[0086] This endstop arrangement is preferred because the bending ofmaterial 8 around the pin 5 downstream of the endstop absorbs some ofthe load along the material 8, making it easier for the endstop tosupport loads on the material 8 after the material 8 has deployed.

[0087] An additional pin 33 could similarly be provided in the energyabsorbers according to the other embodiments if desired.

[0088] In FIG. 12 the endstop 27 used in the first, second, third andfifth embodiments is shown in more detail.

[0089] An alternative arrangement for endstop 34 which could be used inplace of the endstop 27 is shown in FIG. 13. The endstop 34 is formed bya thickening provided by rivets near the end of the material 8.

[0090] A sixth embodiment of the invention is shown in side view inFIGS. 14 and 15, where FIG. 14 shows the energy absorber ready fordeployment and FIG. 15 shows the energy absorber with the material 8fully deployed.

[0091] In the sixth embodiment of the invention a spindle 35 is heldbetween the side plates 1 and 2 and an endstop 36 is provided by an endof the material 8 being passed around the spindle 35 to be doubled backon itself and the doubled over section then being rivetted together. Asthe material 8 is deployed the spiral 15 rotates around the spindle 35.Because the movement of the coil 15 is constrained by the spindle 35there is no requirement for the pin 7.

[0092] Optionally, a shaped insert 37 can be located around the spindle35 to provide a core to the spiral 15 to prevent the spiral 15 deformingduring deployment of the material 8. The optional shaped insert 37 isshown by dashed lines in FIG. 12 only.

[0093] The arrangement of the sixth embodiment is expected to be morelikely to suffer from changes in tension during deployment due to thechange in the radius of the spiral as the material 8 is deployed thanthe other embodiments. This is because the entry angle of the material 8to the pin 5 will change. This can be understood by comprising FIGS. 14and 15.

[0094] A seventh embodiment is shown in side plan view in FIGS. 16 and17 with the energy absorber ready for deployment in FIG. 16 and thematerial 8 fully deployed in FIG. 17.

[0095] The seventh embodiment has the spiral 15 formed around a centralspindle 38 with an endstop 36 similar to that in the fifth embodimentbut instead of having a fixed spindle 35 the spindle 38 is arranged tobe allowed to move in slots 39 formed in the side plates 1 and 2.

[0096] The slots 39 constrain the movement of the spindle 38 moreclosely than in the earlier embodiments employing apertures in the sideplates. The spindle 38 prevents the coil 15 overriding the pin 7 whilethe slot 39 allows sufficient movement of the coil 15 perpendicular tothe direction in which the material 8 is removed from the spiral 15 forthe spiral 15 to float to minimise changes in the geometry and degree ofbending applied to the material 8 as the radius of the spiral 15 changesand so keep the deployment tension as stable as possible.

[0097] A shaped spacer 37 could be used in the seventh embodimentsimilarly to the sixth embodiment.

[0098] In all of the embodiments described above the coil and pins arearranged essentially linearly within the housing. Other arrangements areof course possible. An eighth embodiment is shown in FIG. 18, whichshows a plan view of an energy absorber ready for deployment. The eighthembodiment operates similarly to the seventh embodiment, the main changebeing the displacement of the spiral 15, spindle 38 and slots 39laterally relative to the rest of the absorber structure. This increasesthe width of the energy absorber while decreasing its length in theun-deployed state and increases the degree of bending applied to thematerial 8 as it passes around the pin 5.

[0099] In the eighth embodiment an optional additional pin 24 as shownin the fourth embodiment is used.

[0100] The doubled over and rivetted end structure 36 shown in thefifth, sixth and seventh embodiments to attach the material 8 to thespindle is a simple and convenient arrangement but the person skilled inthe art will realise that there are a very large number of other ways ofattaching a elongate member to a spindle.

[0101] In all of the described embodiments the member 8 is shown as asingle layer of elongate strip material having a constant cross-section.This is a preferred arrangement but it will be realised that other formsof material 8 such as rod or bar forms could be used to form the spiral15. Further, although the use of a strip of material 8 having a constantcross-section is preferred for simplicity and to allow maximum energyabsorption, the use of a varying cross-section may be desirable undersome circumstances such as to provide a lead in portion having a lowerdeployment tension.

[0102] It would of course be possible to replace the single strip ofmaterial 8 with multiple layers of strip material. In particular, thematerial 8 could be formed by a continuous strip doubled over so thatthe material 8 as deployed and as formed into the spiral 15 is formed asa double layer, the strip being folded around a spindle to provide anendstop.

[0103] The pins 5 and 6 in the embodiments depicted in the figures couldeach be the same or differing shapes. For example, they could be roundin cross-section, or some other shape, or they could be integrallyincorporated in some other structure having the functionally of plates 1and 2 and one or more pins. There could be more than two constrainingpins to provide further constraining non-linearity if required in orderto increase the force resisting the movement of material.

[0104] The pins 5 and 6 and also the pin 7 and any optional additionalpins provided can be rollers arranged to rotate about axis that aresubstantially fixed relative to plates 1 and 2 in order to reducefriction when the material 8 is deployed. The friction when the material8 is deployed can also be reduced by providing suitable coatings on thematerial 8 and/or the pins. Alternatively, the material 8 and/or pinsmay be coated in insulating material or plated with a sacrificialmaterial to assist with lubrication and/or provide heat insulation.

[0105] The reduction of friction between the material 8 and the pins,and where appropriate any spindles, is advantageous for a number ofreasons.

[0106] Firstly, when the energy absorber is operating and the material 8is deploying, the absorbed energy is transformed into heat. When theenergy is absorbed by plastic deformation of the material 8 this heatenergy is dispersed throughout the volume of the material 8. However,where the energy is absorbed by friction the heat energy is concentratedat the points of contact between the material 8 and the pins. As aresult, it will generally be the case that the greater the frictionbetween the material 8 and the pins, the higher the proportion of theabsorbed energy will be absorbed by frictional heating and the greaterthe temperatures reached at the contact points between the material 8and the pins will be. If the heating at the contact points issufficiently great contact welding may occur between the material 8 andthe pins resulting in undesirable spikes in the deployment tension andpossibly in failure of the energy absorber.

[0107] Another advantage of minimising the friction between the material8 and the pins is that in general the deployment tension produced bydeformation of the material 8 will be more accurately predictable thanthe tension produced by friction. This is particularly the case wherethe energy absorber is used in fall arrest equipment where it is acommon requirement for the energy absorber to be in place for many yearsbefore operation. Changes in the frictional interaction of the material8 and the pins due to environmental effects over time are lesspredictable and generally greater than changes in the loading producedby deformation of the material 8. As a result, for long term reliabilityit is advantageous to generate as much of the deployment tension aspossible by deformation of the material 8 and to minimise friction.

[0108] The path of movement of the length of material constrained byabutments such as pins 5 and 6 could be any non-linear path. The lengthof material 8 could be any cross section and also such cross sectioncould vary along the length of the material particularly incircumstances in which it is desirable to vary the tension required todeploy such material from its stored condition.

[0109] An alternative arrangement to the above described embodimentswould be a double ended arrangement. This would comprise a housinghaving a end of the material 8 projecting from each end for attachmentto a rigid support or cable. The spiral 15 can be formed by the material8 spiralling inwards, then being folded over and spiralling back outagain. Each end of the material 8 could then be deployed out of thisdouble spiral through a separate pin arrangement as used in one of theembodiments described above.

[0110] In all of the described embodiments the pins are fixed and thedeployment tension is set by the dimensions and physical properties ofthe material 8 and the degree of bending applied to the material 8around the pins 5 and 6, and possibly 7, and it will be understood thatenergy absorbers having different deployment tensions can be provided bychanging the dimensions of the material 8 and the amount of bendingapplied by the pins.

[0111] An energy absorber having a variable deployment tension could beproduced by providing a suitable mechanism, for example a screwmechanism, to allow the position of one or more of the pins to beadjusted.

[0112] A ninth embodiment providing such an adjustable system is shownin FIG. 19.

[0113] The adjustable energy absorber of the ninth embodiment is basedupon the energy absorber of the first embodiment shown in FIGS. 1 and 2.

[0114] In the ninth embodiment the pin 5 is mounted on a slide 40 whichcan be moved by a mechanism, not shown, in the direction of the arrows41 and 42 parallel to the direction of deployment of the material 8 outof the coil 15 towards the pin 5.

[0115] As the slide 40 is moved, the position of the pin 5 relative tothe pin 6 will be altered so that the degree of bending around the pins5 and 6 at points 16 and 17 will also be altered, changing thedeployment tension and amount of energy absorbed by the energy absorber.

[0116] The additional pin 33 as shown in FIGS. 10 and 11 is used to keepthe material 8 moving past the splitter pin 7 in a stable positionregardless of the movement of the pin 5. Thus, the pin 33 assists inkeeping the entry angle of the material 8 to the pin 5 constantregardless of the position of the pin 5, enabling the deployment tensionto be accurately predicted and kept constant during deployment.

[0117] It will be appreciated that other directions of movement of thepin 5 could be used instead of the directions of the arrows 41 and 42 tochange the deployment tension. However, movement parallel to thedirection of deployment in the material 8 out of the coil 15 towards thepin 5 is preferred because this minimises the amount of geometricalchange in the energy absorber as the pin 5 is moved and so simplifiesthe task of ensuring that movement of the pin 5 produces a predictableand consistent change in the deployment tension and that the resultingdeployment tension is constant during deployment.

[0118] In the arrangement shown in FIG. 19 where pins 5, 6 and 7 areemployed it is preferred to have the central pin 5 moveable to minimisethe changes in the geometry at which the material 8 enters and leavesthe pin arrangement when the moveable pin is moved, in order to simplifymatters. If the endstop arrangement is provided by a thickened endstopbeing trapped between the pins 7 and 33, as shown in FIG. 19, it willnot normally be possible to ensure that the moveable pin 5 and pin 6will be able to act as a back-up endstop arrangement unless the possiblerange of movement of the moveable pin is constrained.

[0119] A tenth embodiment of the invention is shown in FIG. 20 in whichthe pins 5 and 6 are spaced apart perpendicular to the deploymentdirection of the material 8 rather than parallel to the deploymentdirection of the material 8.

[0120] In this case, no pin 7 is required, the movement of the coil 15being controlled by a side plate 22 and by contact between the coil 15and the material 8 passing around the pin 6. In this arrangement, wherethe coil 15 contacts the material 8 passing around the pin 6 the coil 15and the material 8 are moving in the same direction, minimisingfriction.

[0121] An eleventh embodiment of the invention is shown in FIG. 21 inwhich the pin 6, pin 7 and side plate 22 are replaced by a single guideelement 51.

[0122] In the eleventh embodiment the energy absorber comprises ahousing formed by plates 1 and 2 (plate 1 only is shown in FIG. 21).Fixing means 50 are provided at one end of the plates for attaching themto a rigid anchor or wire or rope termination. A length of material 8 ofstrip material is formed into a coil 15 and provided with attachmentmeans 9 at one end for attachment to a rigid anchor or wire or ropetermination and with an endstop 27 at the other end. The material 8being located within the housing as before.

[0123] In the eleventh embodiment the length of material 8 passesbetween pin 5 and a guide element 51. The guide element 51 has a curvedguide surface 51 a opposed to the pin 5 which controls the degree ofbending of the material 8 as the material 8 is deployed and ensures thatthe material 8 is bent first in one direction around the pin 5 and thenin a reverse direction in order to maximise the amount of energyabsorbed.

[0124] The guide element 51 also has a curved restraining surface 51 blocated so that when the material 8 deploys the outer surface of thecoil 15 is urged into contact with the restraining surface 51 b. Thecurved retaining surface 51 b controls the position of the coil 15 andprevents it moving towards the pin 5 or sideways similarly to the sideplate 22 of the third embodiment.

[0125] Thus, the guide element 51 acts to split the material 8 away fromthe coil as it deploys and controls the entry angle of material 8 to thepin 5 and guide surface 51 a, thus ensuring that the deployment forceremains constant. Further, the guide element 51 controls the degree ofdeformation of the material 8 with the guide surface 51 a. Finally, theguide 4 element 51 prevents sideways movement of the coil as thematerial 8 deploys. Accordingly, the guide element 51 replaces the pin6, side plate 22 and pin 7 of the previous embodiments.

[0126] The guide member 51 is retained between the side plates 1 and 2by being mounted on two fixed pins 52 and 53 attached to the side plates1 and 2.

[0127] The endstop 27 is a nut and bolt passing through a hole in theend of the strip of material 8 sized so that the nut and bolt cannotpass between the pin 5 and the guide surface 51 a of the guide element51.

[0128] As in the previous embodiments the endstop 27 is sufficientlystrong that after the deployment of the material 8 from the housing hasbeen stopped by the endstop 27 the energy absorber will still be able tosupport twice the peak tension force encountered during deployment.

[0129] A twelfth embodiment of the invention is shown in FIGS. 22 to 24.

[0130] In this case the energy absorber structure does not employ sideplates. A length of material 8 which in this case is a rod material iswound into a helical coil. The free end of the length of material 8 isprovided with attachment means for attaching to a rigid anchor or ropeor wire termination and has an endstop 27 at the other end to preventthe material 8 being separated from the rest of the energy absorber. Inthe figures this attachment means are not shown.

[0131] The material 8 passes between a pair of spaced apart parallelside plates 54 and 55 which define a channel between them through whichthe material 8 can pass and the side plates 54 and 55 also have a pin 56mounted between them.

[0132] A fixing means for attaching the side plates 54 and 55 to a rigidanchor or wire or rope termination is provided by a further plate 57which links the side plates 54 and 55 to a load ring 58 which can beattached to a rigid anchor or to a wire or rope.

[0133] When the energy absorber is required to absorb energy an increasein tension force is applied to the load ring 58 and to the material 8until the applied force becomes sufficiently high to pull the material 8around the pin 5 such that the absorber extends and is plasticallydeformed to absorb energy. A guide pin 59 projects from the side plate54 into the interior of the helical coil. The guide pin 59 is in contactwith the inner surface of the coil on the opposite side of the pin 56 tothe entry direction of the material 8 when pulling of the material 8over the pin 56 occurs so that the guide pin 59 counteracts and resiststhe tendency for the axis of the helical coil to move relative to thepin 56 and therefore ensures a constant degree of yielding of thedeployed material 8 so that the deployment force remains constant.

[0134] The endstop 27 is formed by a nut tightened onto a threaded endsection of the material 8. However, the nut could be replaced by athickened end section of the material 8. The nut 27 is too large to fitbetween the side plates 54 and 55 so that when the nut 27 contacts theside plates 54 and 55 deployment of the material 8 is stopped.

[0135] In the illustrated embodiment the plate 57 projects between theside plates 54 and 55 to define a narrow channel between the end of theplate 57 and the pin 56 so that the endstop 27 cannot pass between thepin 56 and the end of the plate 57. This provides a secondary back-upendstop for the energy absorber.

[0136] The endstop arrangement is shown in the condition where theendstop has stopped deployment of the material 8 by coming into contactwith the side plates 54 and 55 in more detail in FIG. 24.

[0137] Similarly to previous embodiments the endstop 27 is arranged sothat when the endstops have stopped deployment of the material 8 theenergy absorber is able to support double the peak deployment load.

[0138] A thirteenth embodiment of the invention is shown in FIGS. 25 and26.

[0139] The thirteenth embodiment of the invention is similar to thetwelfth embodiment of the invention in that the material 8 is a rodmaterial formed into a helical coil. However in the thirteenthembodiment the helical coil is arranged with the coil axis substantiallyparallel to the direction of the applied force causing the material 8 todeploy whereas in the twelfth embodiment the coil axis was perpendicularto the applied force direction.

[0140] In the thirteenth embodiment the energy absorber comprises asubstantially U-shaped plate 60 on which a pair of pins or rollers 61and 62 are mounted. The pins 61 and 62 are mounted on perpendicularfaces of the U-shaped plate 60 so that the axes of the pins 61 and 62are perpendicular.

[0141] The plate 60 is linked to fixing means provided by a load eye 58for connection to a rigid anchor or wire or rope termination similarlyto the twelfth embodiment while the free end of the deployable material8 is provided with an attachment means, not shown, for attachment to arigid anchor or wire or rope termination and has an endstop, not shown,at the other end to prevent the deployable material 8 being separatedfrom the rest of the energy absorber.

[0142] When the energy absorber is required to absorb energy an increasein tension force is applied between the load eye 58 and the free end ofthe deployable material 8 until the applied force becomes sufficientlyhigh to pull material 8 around pins 61 and 62 so that the absorberextends to absorb energy. The deployable material 8 is first bent aroundthe pin 61 which has an axis substantially parallel to the axis of thehelical coil and is subsequently bent in a second directionperpendicular to the first about the pin 62 having an axis perpendicularto the axis of the pin 61 and the helical coil. The material 8 thenpasses through an aperture 63 in the U-shaped plate 60.

[0143] A guide element 64 projects from the U-shaped plate 60 and bearson the inner surface of the helical coil. Similarly to the pin 59 of thetwelfth embodiment the guide element 63 prevents movement of the helicalcoil relative to the pin 61.

[0144] Similarly to the twelfth embodiment the endstop can be formed bya nut screwed onto a threaded end of the deployable material 8 or athickened end portion. The size of the endstop is such that the endstopcannot pass through the channel defined between the pins 61 and 62 andthe adjacent surfaces of the U-shaped plate 60. Further, the endstop ispreferably sized so that it cannot fit through the aperture 63 so theaperture 63 can form a back-up endstop.

[0145] The endstop must be sufficiently strong to retain the material 8attached to the energy absorber under a load at least double thedeployment tension force after full deployment of the material 8.

[0146] A fifteenth embodiment of the invention is shown in FIGS. 27 and28.

[0147] The fifteenth embodiment is similar to the thirteenth embodimentin that the deployable material 8 is a rod material arranged in ahelical coil. The energy absorber has a structure comprising a bodyformed by a pair of parallel spaced apart side plates 70 and 71 with apair of parallel pins 73 and 74 located between them. Similarly to thethirteenth embodiment the plates 70 and 71 are connected to a load eye58 for attachment to a rigid anchor wire or rope termination. The lengthof material 8 is provided with attachment means, not shown, at one endfor attaching to a rigid anchor or wire rope termination and with anendstop at the other end of the material 8 being separated from the mainbody.

[0148] When the energy absorber is required to absorb energy an increasein tension force is applied between the load eye 58 and the material 8until the applied force becomes sufficiently high to pull the material 8around pins 73 and 74 such that the absorber extends to absorb energy.The material 8 passes first around the pin 73 which bends the material 8in a first direction and then around the pin 74 which bends the material8 in the opposite direction, so maximising the amount of energyabsorbed.

[0149] The pins 73 and 74 have axes parallel to the axis of the helicalcoil of deployable material 8.

[0150] In order to prevent movement of the helical coil relative to thepins 73 and 74 an extension of the plate 71 is provided with an aperture71 a through which the deployable material passes before reaching pins73 and 74.

[0151] An endstop is provided by a nut screwed onto a threaded endsection of the deployable material 8 or by an increased diameter endportion of the deployable material 8 with the endstop portion being toolarge to pass through the aperture 71 a.

[0152] As before, the endstop arrangement must be sufficiently robustthat after deployment of the material 8 has been stopped by the endstopthe energy absorber is able to support a load at least double thedeployment load.

[0153] If it is desired to keep the deployment tension of the energyabsorber constant but to change the total amount of energy absorbed orlimit the maximum links of the energy absorber after deployment to aparticular value the length of the material 8 can be varied accordingly.

[0154] In most of the described embodiments, two pins 5 and 6 are usedto carry out bending of the material 8 in a first sense and then back inthe opposite sense and to absorb energy with a further pin 7 being usedto separate the material 8 from the coil. In the described embodimentsthe pin 7 and any additional optional pins employed are not intended tocarry out a significant amount of the bending of the material 8. Itwould of course be possible to employ more pins to bend the material 8further if desired. However, it is preferred to only bend the material 8once in each sense in order to avoid repeated bending and re-bending ofthe material 8 which could weaken the structure of material 8 andprevent the material 8 reliably supporting twice the deployment tension.

[0155] It has been found that it is particularly useful to form thematerial 8 from stainless steel, particularly stainless steel 316.

[0156] Where the energy absorber is to be employed in a fall arrestsystem and the material 8 is a strip it has been found that thestainless steel strip should have a thickness of at least 2 mm and awidth of at least 30 mm. If a strip having smaller dimensions is used ithas been found to be difficult to securely attach the end of thematerial 8 to a rigid anchor or cable or to provide a reliable endstop.

[0157] It is preferred that the diameter of the inner surface of thespiral coil 15 be at least 40 mm. If the spiral coil is coiled down to asmaller inner radius, the changes in geometry as the material deploysmay cause changes in the deployment tension.

[0158] A wide range of materials can be used to provide the pins.However, it is preferred to employ stainless steel rollers as pins withthe rollers or the deployable material having a friction reducingsurface coating of molybdenum disulphide or a similar material or afriction reducing layer such as silver plating or a similar metalplating layer.

[0159] In many of the described embodiments a first pin 5 is used tobend the material 8 being deployed and the material 8 is then bent inthe opposite direction by a second pin 6 to straighten it. Thisre-bending by the second pin 6 increases the amount of energy absorbedby the material 8 and so increases the amount of energy that can beabsorbed by the energy absorber. The second pin 6 also helps tostabilise movement of the material 8 and so helps to keep the deploymenttension constant during deployment. Finally, the pin 6 helps to hold thematerial 8 in place before deployment occurs.

[0160] Although lateral movement of the free end of the material 8before deployment is not of any real consequence for the operation ofthe energy absorber, it has been found that in practice, particularlywhen the energy absorber is used in a fall arrest system, users can findeasy or excessive lateral movement of the free end of the material 8alarming.

[0161] Accordingly, although the use of the second pin 6 is notessential it is preferred in practice because it allows the energyabsorber to absorb more energy and makes the energy absorber moreacceptable to users.

[0162] It will be understood that in order to allow the energy absorberto absorb large quantities of energy it is necessary for the bending ofa material 8 to be sufficient to cause plastic deformation of thematerial 8.

[0163] Where an energy absorber is to be used in a fall arrest system itis desirable, and in many countries a legal requirement, that when afall arrest event occurs so that the energy absorber operates and thematerial 8 is deployed a clear visual signal that such deployment hasoccurred is provided.

[0164] One method of providing such a visual indication of operation inany of the described embodiments or options is shown in FIGS. 29 and 30in which FIG. 29 shows the energy absorber in its normal condition andFIG. 30 shows the energy absorber when the material 8 has been deployed.

[0165] The energy absorber is retained inside a weather proof housing 43having a contrasting coloured section 44.

[0166] A shroud 45 is attached to the material 8 and is positioned sothat normally the shroud 45 covers the contrasting coloured section 44of the housing.

[0167] When the energy absorber has operated and the material 8 isdeployed from the housing the shroud 45 is moved off the contrastingcoloured section 44 so that it can be seen.

[0168] Thus, exposure of the contrasting coloured section 44 provides anunambiguous visual indication that the energy absorber has beenoperated. In a fall arrest system this indicates that a fall arrestevent had occurred.

[0169] Typically, the normally visible parts of the housing 43 andshroud 45 would be black while the contrastingly coloured section 44would be yellow, red or a metallic colour.

[0170] A reverse arrangement where the contrasting coloured portion iscarried with the material 8 as it deploys so that the contrastingcoloured portion is removed from a fixed shroud or cover to reveal itwould also be possible.

[0171] Finally, the material 8 itself could be coloured to provide thevisual indication when it was deployed. However, the use of a separatecoloured portion to provide the visual indication is preferred.

[0172] Where an external housing is employed on the energy absorber, asshown in FIGS. 3, 29 and 30, the housing can be used to replace theU-shaped plate 22 in limiting movement of the spiral coil 15, providedthat the housing is strong enough and provided with a suitable internalprofile.

[0173] As explained above, if the angle through which the deployedmaterial 8 changes the required deployment force will also change. Infall arrest systems the maximum deployment load is set at a level whichwill not cause significant injury to a falling user and will notoverstress other parts of the fall arrest system such as end anchors,intermediate anchors and cables and their supporting structures.Further, by arranging the deployment load to be constant and as close aspossible to the maximum permitted load the rate at which energy isabsorbed by the energy absorber can be maximised so that the durationand distance of a fall event can be reduced as far as possible.Accordingly, it will be understood that the deployment load must be asnearly constant as possible and that unpredictable variations in thedeployment load must be avoided.

[0174] Accordingly, it is necessary to ensure that the entry angle atwhich the deployable material approaches the first pin, or other bendingelement, is kept as constant as possible and in the describedembodiments various restraining and guiding arrangements for doing thisare described.

[0175] Where a spiral coil is used it will be appreciated that if theaxis of rotation of the spiral coil is fixed the entry angle to thebending or deforming elements of the energy absorber will inevitablyalter as the material is deployed because the radius of the coil willchange. Accordingly, where a spiral coil is used it is preferred thatthe coil be free to float while the entry angle of the material to thematerial bending parts of the energy absorber is restrained so that thebody of the coil can move laterally to allow the entry angle to remainconstant as the radius of the spiral coil reduces.

[0176] In the embodiments above it is specified that the endstop isarranged such that the energy absorber is able to support a load of atleast double the deployment load when deployment of the deployablematerial has been stopped by the endstop. It will be appreciated that inthe embodiments described, the stopping point of the endstop is arrangedupstream of the pins or elements used to bend the deployable material.As a result, it should be appreciated that because of the well knowncapstan effect the load actually applied to the endstop will be lowerthan the load acting on the energy absorber as a whole. As a result,although the energy absorber must be able to support at least double thedeployment load it does not automatically follow that the endstop itselfwould be able to support double the deployment load if it was applieddirectly.

[0177] In the description the use of pins to control movement of and tobend the deployable material is described. It will be realised that aswell as fixed or rotating pins or rollers being used the function of thepins could be replaced by suitably shaped fixed elements, particularlyfixed elements formed of plastics material.

[0178] Although the invention has been particularly described above withreference to specific embodiments, it will be understood by personsskilled in the art that these are merely illustrative and thatvariations are possible without departing from the scope of the claimswhich follow.

1. An energy absorber comprising housing means, a store of plasticallydeformable material wound in a coil and having an endstop at one end andmounted in said housing means, means for attaching the energy absorberto a first structure, means for attaching the plastically deformablematerial to a second structure, and means responsive to a predeterminedtensile load between the first and second structures effective to deploysaid plastically deformable material in a controlled manner from itsstore whereby said material is permanently plastically deformed duringsaid deployment, thereby absorbing energy, the energy absorber beingable to support a load at least twice the predetermined tensile loadwhen further deployment of said material is prevented by the endstop. 2.An energy absorber as claimed in claim 1 wherein the energy absorberforms a part of a fall arrest system.
 3. An energy absorber as claimedin claim 1 or claim 2 wherein the plastically deformable material is alength of yielding material such as metal, the length being relative tothe maximum extension required for absorbing energy.
 4. An energyabsorber as claimed in any preceding claim wherein one end of the lengthof material has provision for attaching the material to an elongatesafety element or an anchorage.
 5. An energy absorber as claimed in anypreceding claim wherein the housing means has provision for attachmentto an elongate safety element or an anchorage.
 6. An energy absorber asclaimed in any preceding claim wherein the length of material has across-sectional configuration selected from the group consisting ofrectilinear, round, tubular or a combination of the foregoing.
 7. Anenergy absorber as claimed in claim 6, wherein the length of material isa strip having a rectilinear cross-section.
 8. An energy absorber asclaimed in any preceding claim wherein the configuration of theplastically deformable material varies along its length.
 9. An energyabsorber as claimed in any preceding claim wherein the non-linear pathof the material when pulled and as constrained by the housing means isdefined by two-dimensional inclinations.
 10. An energy absorber asclaimed in any preceding claim wherein the elements of the housing meansconstraining the path of movement of the material when pulled relativeto the housing means are selected from the group consisting of circularshafts or rollers, or any other shape constraining the path of thematerial.
 11. An energy absorber as claimed in claim 10 wherein theelements of the housing means constraining the path of movement of thematerial when pulled relative to the housing means are rollers, eachroller rotating about its own axis.
 12. An energy absorber as claimed inclaim 10 or claim 11, wherein the path of movement of the material isconstrained to bend the material in a first sense about a first circularshaft or roller, and then to bend the material in a second senseopposite the first about a second shaft or roller.
 13. An energyabsorber as claimed in any one of claims 9 to 12, wherein the non-linearpath of the material can be varied to alter the predetermined tensileload.
 14. An energy absorber as claimed in claim 13, when dependent onone of claims 10 and 11 in which the position of one of the circularshafts or rollers can be changed to alter the predetermined tensileload.
 15. An energy absorber according to any preceding claim, whereinthe coil of plastically deformable material rotates as the material isdeployed and is free to move in a plane perpendicular to an axis of itsrotation.
 16. An energy absorber as claimed in claim 15, wherein themovement of the coil in a plane perpendicular to its axis of rotation isrestrained so that the orientation of the deformable material relativeto a means for plastically deforming the material remains substantiallyconstant during deployment of the material.
 17. An energy absorber asclaimed in any preceding claim wherein the material is stainless steel.18. An energy absorber as claimed in claim 17, wherein the material isstainless steel
 316. 19. An energy absorber as claimed in any precedingclaim wherein the material has a friction reducing surface coating orlayer.
 20. An energy absorber as claimed in claim 10 or claim 11,wherein the shafts or rollers have a friction reducing surface coatingor layer.
 21. An energy absorber as claimed in any preceding claimwherein the coil is a spiral coil.
 22. An energy absorber as claimed inany one of claim 1 to 20 wherein the coil is a helical coil.
 23. Anenergy absorber as claimed in any preceding claim, in which the energyabsorber further comprises a visually distinctive element arranged to beexposed when the material is deployed to provide a visual indicationwhen the material is deployed.
 24. An energy absorber substantially asshown in or as described herein with reference to FIGS. 1 and 2; FIGS. 3and 4; FIGS. 5 and 6; FIGS. 7, 8 and
 9. FIGS. 10 and 11, FIGS. 14 and15, FIGS. 16 and 17, FIG. 18, FIG. 19, FIG. 20; FIG. 21; FIGS. 22 to 24;FIGS. 25 and 26; FIGS. 27 and 28; or FIGS. 29 and 30 of the drawings.